Decorative overlays of silver and other metals have been applied to glass and other electrically non-conductive surfaces in the past, but these have not been entirely satisfactory because of the poor adhesion of the metal plating to the glass or other non-conductive material such as plastic. Generally speaking, such metal patterns have been applied by hand, e.g. with brushes, by silk screening, or by metal leaf. The metal is held on the non-conductive surface by an adhesive, and when the surface of the metal is rough, such as with brush application, the metal cannot be adequately polished without damaging the metal pattern.
The metal pattern has also been applied by electroplating, and in such method, conductive areas in the shape of the desired pattern are formed on the base, non-conductive material or substrate. Such areas must withstand the inherent stresses of the electric current and the plating solutions, e.g. acidic or cyanic solutions, and maintain a strong bond with the base material after being subjected to such solutions.
To be visually and artistically acceptable, the metal pattern must have sharp boundaries and should cover at least 50% of the decorated surface when applied as a decoration to various decorative items, such as, vases, bowls, decanters, plastic pens, picture frames, paper weights, coasters, etc.
It is know in the art to apply a rough, porous metal-glass or metal-ceramic frit with an abrasive to a non-conductive base material or substrate in a pattern and to fuse the mixture to the substrate for the purpose of providing heating elements on glass. See U.S. Pat. No. 3,703,445. As described in the patent, surface metal is applied to the so applied and fused frit pattern by electrolysis deposit, and the frit pattern, by itself, is rough and is not sufficiently conductive for electroplating. Therefore, the frit pattern must be subjected to electroless deposit before electroplating. Furthermore, the patent teaches that the use of masking is unsatisfactory.
The method of the invention provides an aesthetic decorative metal pattern on a non-conductive substrate, such as glass or plastic, by first producing a layer of an electrical conductivity sufficient for electroplating by conventional electroplating methods in the shape of the desired pattern on an electrically non-conductive substrate. The pattern normally has a surface area at least equal to 50% of the surface area of the substrate, and such layer comprises a material which fuses with the substrate upon heating to the fusion temperature of such material and forms an intermolecular bond with the substrate. For example, if the substrate is glass, the material is a glass frit which forms such bond with the substrate. If the substrate is a plastic, the material is a plastic metal mixture which so bonds to the substrate.
The layer also comprises finely divided metal, e.g. silver, copper, etc., of high conductivity in an amount, e.g. at least 50% by volume of the material which bonds to the substrate, which will provide the layer with an electrical conductivity sufficient for electroplating by conventional methods.
After the first layer is bonded to the substrate, a second layer of finish metal, i.e. the metal of the pattern to be observed by the eye, e.g. silver or gold, is applied to the first layer by electroplating. If desired, the first layer can be coated with a layer of a highly conductive metal, e.g. silver, by electroplating prior to the electroplating of the finish metal.
The finished metal pattern can be intricate and has sharply defined edges. The metal pattern can be intricate and has sharply defined edges. The metal pattern has a smooth surface which, if necessary, can be polished. The method provides a strong bond of the pattern with the substrate which not only permits polishing but also withstands the stresses of the electroplating conditions.
In accordance with the preferred method of the invention, a masking resist is first applied to those areas of a glass surface which are not to be plated. The resist consists of a material which will adhere to the glass during the subsequent step of applying a frit solution, as described hereinafter, but which will detach from the substrate during fusing of the frit with the substrate by heating, such as by oxidation of the mask material which turns to ash. The resist can, for example, be paper or a thermoplastic, such as vinyl, with adhesive on the face thereof which engages the glass article or be a rubbery plastic between two layers of paper, the surface which is to engage the glass article bearing an adhesive to hold the resist in place by the adhesive and which is covered by a release sheet, the release sheet being removed before the application of the resist.
Of course, the resist covers the area of the article which is not to be plated with the metal. The resist can be die cut or otherwise formed, and is sufficiently formable to be applied to non-linear or non-planar surfaces.
After the resist is applied, a frit solution is applied to the resist and to the spaces where the pattern is to appear. The frit solution comprises a metal in finely ground form and in an amount sufficient to make the pattern continuously conductive after fusing, a finely ground glass which will fuse with the substrate, such as borosilicate glass, and a carrier, such as pine oil. Preferred solutions, for silver plating comprise a frit-containing solution which can be sprayed, or otherwise applied, and consist of, by volume, about 4.5% borosilicate glass, 70% of silver and the remainder pine oil or 8% borosilicate glass, 68% silver and remainder pine oil. The silver and borosilicate are in particulate form and have a particle size the range from 300-400 mesh. The solutions can be diluted by adding up to 50% of a mixture of turpentine and mineral spirits as may be required for application.
The article with the resist and frit thereon are then subjected to heating, such as in a furnace at a temperature which will cause the glass of the frit to melt and fuse with the glass of the substrate without causing flow or slumping of the substrate glass. Such temperature can, for example, be in the range of from about 1000xc2x0 F. to about 1100xc2x0 F. and preferably, 1060xc2x0 F. During the heating, the resist bums away and the frit solvent is evaporated leaving a continuously conductive pattern molecularly linked and strongly bonded to the substrate and with sharply defined edges.
After cleaning in a conventional manner in preparation for plating, the article is placed in a plating tank containing the electrolyte and an electrode which will provide the desired pattern surface, e.g. silver and is electroplated in a conventional manner.
With substrates which cannot withstand the fusing temperature of glass, such as plastics, e.g. a polycarbonate, a know type of metal loaded plastic compound without frit, such as the metal-loaded plastic paste which has been sold by Enthone-OMI Incorporated, West Haven, Conn., under the trademark ENTHONE, which becomes bonded to certain plastics and becomes electrically conductive when cured by heating, can be used in place of the frit-containing solution described hereinbefore, the temperature of heating being much lower, e.g. in the range of about 230xc2x0-250xc2x0 F. The metal-loaded past is applied in a continuous pattern to the plastic article and cured by heating which causes the paste to harden and chemically and intermolecularly bond to the article. The hardened pattern is then subjected to a vigorous, conventional cleaning/activating treatment, and the article is briefly immersed in a conventional silver strike plating solution. Thereafter, the pattern is electroplated in a conventional manner to build up a layer of the desired metal on the pattern. Such layer can, for example, have a thickness of about 0.003 of an inch.
When the pattern is to be applied to the flat or slightly domed surface of a non-conductive article, it may be preferable to apply the material of the first layer which is to be heated and then plated to such surface by silk screening or pad printing. Such application of the material is faster and more cost-effective for the decoration of articles such as picture frames and paperweights.